Draining these peatlands for agriculture, or reduced rainfall due to climate change, would release massive amounts of planet-warming greenhouse gases, they warned in a study published in Nature magazine.

"We found 30 billion tonnes of carbon that nobody knew was there," said Simon Lewis, co-lead author of the study and a professor at the University of Leeds.

"If the Congo Basin peatlands were to be destroyed, it would release billions of tonnes of CO2 into the atmosphere," he told AFP. "Keeping that carbon locked up" should be a priority."

Peatlands are carbon-rich ecosystems that cover three percent of Earth's land surface, but store about a third of all soil carbon.

Most peat - dense, dark-brown muck composed of decaying plants - is located in Canada, Scandinavia and Siberia, but the tropics hold large stores as well.

Until the mid-20th century, it was often cut into bricks, dried and burned as a fuel.

More recently, however, scientists have understood that peatlands, which are at least a food (30 centimeters) thick, harbor vast stores of carbon in the form of the greenhouse gases that are driving global warming.

The Congo Basin peatland averages about six feet (2 meters) in thickness.